1. Field of the Invention
This invention relates generally to amphibious aircraft, and more particularly, to a multi-hulled aircraft boat (hereinafter "flying boat") capable of V-STOL (Vertical Short Take-Off and Landing) operations.
2. Description of the Prior Art
In the aerospace industry, it has long been desirous to produce practical and efficient aircraft capable of vertical take-off and landing, thus obviating the need for expansive airports required by conventional aircraft. Because a conventional aircraft's take-off and landing performance is dictated by its stalling speed, the speed at which the wings' angle of attack will cause sufficient separation and turbulent air flow that it will cease to provide adequate lift, such an aircraft requires runways of sufficient length such that take-off and landing rollouts can be performed with adequate safety margins. Over the last several decades, advances in aerodynamic technology, such as slotted wing flaps and slats and surface blowing, have resulted in lowering the stalling speeds of high performance aircraft, consequently providing them with higher safety margins and allowing the operation of larger aircraft from smaller runways. Nevertheless, the quest for aircraft capable of vertical take-off and landing has spawned a large array of unusual configurations, ranging from the conventional helicopter to the state of the art Bell-Boeing V-22 Osprey tilt rotor and McDonnell-Douglas AV-8B Harrier II.
The most common configuration of vertical take-off and landing aircraft is the helicopter. The helicopter is capable of true vertical flight, including the ability to hover in place, fly forward and aft, and from side to side. Unfortunately, the helicopter has many limitations, the most significant thereof being its mechanical complexity and high operational expense. Moreover, the principles of aerodynamics result in obvious limitations on performance, most notably the low maximum attainable forward velocities and reduced range when compared with fixed wing aircraft, attributable to the high drag and structural limits of the rotor system and high power to payload ratio.
One notable helicopter derivative that has generated considerable interest with the U. S. military is the Bell-Boeing V-22 Osprey, actually a hybrid aircraft which combines the vertical mobility of a helicopter with the cruising speed of a turboprop transport. This unique aircraft is actually a derivative of the Bell XV-15, developed pursuant to a U.S. Army contract in 1972. It comprises a pair of tiltable rotor units which are mounted on each wing tip, each capable of being rotated at varying angles of incidence relative to the aircraft itself, such that vertical take-off and landing and the transitions therebetween may be accomplished. While this design is fairly practical, it has some serious drawbacks, the most serious thereof being the necessity to cross-shaft both engines in the event of an engine failure to eliminate asymmetrical thrust and consequent loss of control, and the high moments of inertia that need be overcome along the aircraft's roll axis, resulting in sluggish turning performance and overall reduced maneuverability. Because of the cross-shafting requirement and the outboard wing location, this power plant configuration results in a higher dry weight by virtue of the extensive transmission hardware and stronger wings required to support such a design.
Similar aircraft in this area, such as the tilt wing Boeing Vertol Model 76, are even more complex and have experienced such problems as wing stalling during the transition between vertical and conventional flight.
Yet another notable design in this area is the Doak X-16, a tilt duct aircraft having a pair of ducted fans disposed on opposite wing tips similar to the configuration of the Bell Boeing V-22 Osprey, and obviously having similar disadvantages.
The present invention is directed to a V-STOL flying boat which is capable of making the transition from vertical to conventional flight without the need for heavy and complex cross-shafting and which, by virtue of its power plant location, lifting body type fuselage, and smaller wing, results in enhanced performance.